JP2018507138A - Underwater vehicle design and control method - Google Patents

Abstract

A vehicle designed to use ground effect forces and control the positioning of the vehicle with respect to a surface, as well as a method of using the same, is described. In one embodiment, a vehicle has a vehicle body that includes a first portion having a partial oval shape and a second portion that is flat and associated with the first portion. The vehicle also includes one or more sensors configured to sense information from a suitable surface toward which the flat second portion of the vehicle body is oriented. In yet another embodiment, the vehicle has a vehicle body that includes a flat portion and at least one thruster associated with the flat portion of the vehicle body. At least one thruster has a certain diameter and a certain thrust capacity.

Description

(Government-funded)
This invention was made with government support under grant number CMMI1363391, subsidized by the National Science Foundation. The government has certain rights in the invention.

(Cross-reference of related applications)
This application is filed in US Provisional Application No. 62 / 127,510 filed March 3, 2015 and US Provisional Application No. 62 / 127,489 filed March 3, 2015. S. C. § 119 (e) claims the benefit of priority, the disclosure of each of which is hereby incorporated by reference in its entirety.

  The disclosed embodiments relate to underwater vehicle design and control methods.

  In marine robotics, much research has been done to develop advanced systems for inspection and maintenance of structures. For example, applications for such vehicles include inspection of underwater infrastructure, pipelines, dams, oilfield drilling rigs, and boiling water reactor internal systems, to name a few. In addition, these inspections require both proximity visual inspection and contact inspection to test for external and internal structural defects. In other applications such as port security, careful contact ultrasonic scanning and visual visualization of the hull to prevent contraband smuggling is a field of great interest. Currently, the US Navy's multi-million-marine marine mammal program employing human divers and dolphins is often required to take on such dangerous missions. However, these programs are not easily extensible. Substantial effort is currently devoted to undersea robotics to reduce the risk to human divers and find scalable solutions. However, a typical flooded surface inspection robot is a large and complex system that uses various combinations of steering wheels, magnets, and / or vacuum suction to move across the flooded surface. The effort required to control these systems is enormous and these systems are often tethered. Therefore, the resulting inspection process is slow and does not have the discreteness required for various types of detection.

  In one embodiment, a vehicle has a vehicle body that includes a first portion having a partial oval shape and a second portion that is flat and associated with the first portion. The vehicle also includes one or more sensors configured to sense information from a surface toward which the flat second portion of the vehicle body is oriented.

  In another embodiment, a vehicle includes a vehicle body including a flat portion and one or more sensors configured to sense information from a surface toward which the flat portion of the vehicle body is oriented. Have. The sensor has a desired sensing range from a flat portion of the vehicle body. Furthermore, the chord length of the flat part of the car body provides at least one stable equilibrium position relative to the surface within the desired sensing range when the vehicle is moved laterally with respect to the surface.

  In yet another embodiment, the vehicle has a vehicle body that includes a flat portion and at least one thruster associated with the flat portion of the vehicle body. At least one thruster has a certain diameter and a certain thrust capacity. The vehicle also includes one or more sensors that are configured to sense information from a surface toward which a flat portion of the vehicle body is oriented. The sensor has a desired sensing range from a flat portion of the vehicle body. Further, the diameter of the at least one thruster is appropriately sized and the thrust capacity is sufficient to provide at least one stable equilibrium position within the desired sensing range when the vehicle is located adjacent to the surface. It is.

  In another embodiment, a method of controlling a vehicle immersed in a fluid includes positioning the vehicle immersed in a fluid at a first preselected distance relative to a surface; and Applying a ground effect force to the vehicle to maintain the selected distance.

  In yet another embodiment, a method of controlling a vehicle immersed in a fluid includes applying a ground effect force to the vehicle at a first stable equilibrium distance of the ground effect force against a surface, so that the vehicle When displaced relative to the surface, the ground effect force biases it towards the first stable equilibrium distance.

  In another embodiment, a method for controlling a vehicle immersed in a fluid includes directing a flat portion of the vehicle toward a surface and applying a thrust to the vehicle to bias the vehicle toward the surface. Applying a ground effect force to the vehicle against the surface, wherein the net weight of the vehicle, the net thrust force urging the vehicle toward the surface, and the ground effect force associated with the surface are oriented toward the surface Providing a substantially zero force applied to the vehicle in the direction to be applied.

  It should be understood that the foregoing concepts and additional concepts discussed below may be arranged in any suitable combination, as the disclosure is not limited in this respect. Furthermore, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures.

  In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference contain discrepancies and / or inconsistent disclosure with respect to each other, the document with the later effective date shall prevail .

  The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For clarity purposes, not all components can be labeled in all figures.

FIG. 1A is a schematic top view of one embodiment of a partially elliptical vehicle with a flat bottom including thrusters and sensors. FIG. 1B is a side view of the embodiment of the vehicle shown in FIG. 1A. 1C is a bottom view of the embodiment of the vehicle shown in FIG. 1A. FIG. 2A is a schematic top view of one embodiment of a partially elliptical vehicle where the flat bottom includes a thruster and a sensor. FIG. 2B is a side view of the embodiment of the vehicle shown in FIG. 2A. 2C is a bottom view of the embodiment of the vehicle shown in FIG. 2A. FIG. 3 is a bottom view of a partially elliptical vehicle with a flat bottom including labeled dimensions. FIG. 4 is a side view including the labeled dimensions of the vehicle shown in FIG. FIG. 5 is a side view of a partially elliptical vehicle including a dimension with a flat bottom labeled. FIG. 6 is a schematic representation of an elliptical vehicle that traverses a surface with one or more irregularities. FIG. 7 is a schematic representation of an elliptical vehicle that traverses a curved surface. FIG. 8A is a schematic representation of a vehicle moving laterally relative to the surface in a region where upward ground effect is present. FIG. 8B is a schematic representation of the forces acting on the vehicle of FIG. 8A. FIG. 9A is a schematic representation of a vehicle moving laterally with respect to the surface in a region where a downward suction ground effect is present. FIG. 9B is a schematic representation of the forces acting on the vehicle of FIG. 9A. FIG. 10A is a schematic representation of a vehicle including a central thruster in free flow conditions. FIG. 10B is a schematic representation of the forces acting on the vehicle of FIG. 10A. FIG. 11A is a schematic representation of a vehicle including a central thruster within the distance of the surface where the ground effect force exists. FIG. 11B is a schematic representation of the forces acting on the vehicle of FIG. 11A. FIG. 12A is a top view of one embodiment of a vehicle including a pump and a plurality of thrusters oriented in different directions. 12B is a cross-sectional side view of the vehicle of FIG. 12A illustrating the arrangement and orientation of the thrusters along different portions of the vehicle. FIG. 13A is a top view of one embodiment of a vehicle including a pump and a plurality of thrusters oriented in different directions. 13B is a cross-sectional side view of the vehicle of FIG. 13A illustrating the arrangement and orientation of the thrusters along different portions of the vehicle. FIG. 14A is a top view of one embodiment of a vehicle including a pump and a plurality of thrusters oriented in different directions. 14B is a cross-sectional side view of the vehicle of FIG. 14A illustrating the arrangement and orientation of the thrusters along different portions of the vehicle. FIGS. 15-18 are schematic representations of a vehicle including a variable center of gravity used to orient a flat portion of the vehicle toward surfaces oriented at different angles. FIGS. 15-18 are schematic representations of a vehicle including a variable center of gravity used to orient a flat portion of the vehicle toward surfaces oriented at different angles. FIGS. 15-18 are schematic representations of a vehicle including a variable center of gravity used to orient a flat portion of the vehicle toward surfaces oriented at different angles. FIGS. 15-18 are schematic representations of a vehicle including a variable center of gravity used to orient a flat portion of the vehicle toward surfaces oriented at different angles. FIG. 19 is a flow diagram of one possible embodiment of a control method for a vehicle to maintain a desired distance relative to a surface using ground effect forces. FIG. 20 is a graph of force versus gap size for a vehicle that includes an asymmetric body that is moved laterally relative to the surface. FIG. 21 is a graph of force versus gap size for a vehicle that includes an asymmetric body that is moved laterally relative to the surface at a smaller gap size. FIG. 22 is a graph of lift versus speed calculated for different gap sizes. FIG. 23 is a graph of lift versus speed measured for different gap sizes. FIG. 24 is a graph of vehicle displacement and speed around a stable equilibrium position with respect to the surface when the vehicle is initially displaced by 1 mm. FIG. 25 is a graph of the lift coefficient for different sized vehicles at different ε values moving at 0.5 m / sec relative to the surface. FIG. 26 is a graph of lift coefficient for different sized vehicles at different ε values moving at 1.0 m / sec relative to the surface. FIG. 27 is a graph of drag versus speed. FIG. 28 is a graph of drag coefficient for different ε values. FIG. 29 is a graph of lift coefficient vs. λ. FIG. 30 is a graph of applied voltage versus applied voltage for the pump. FIG. 31 is a graph of the force applied by the thruster to the vehicle at different gap values relative to the surface. FIG. 32 is a graph of the force applied by the thruster to the vehicle at different gap values relative to the surface, calculated for different applied thruster voltages. FIG. 33 is a graph of the experimental force applied by the thruster to the vehicle at different gap values relative to the surface for different applied thruster voltages. FIG. 34 is a graph of stable balanced distance versus different applied thruster voltages. FIG. 35 is a graph of normalized reflectivity versus applied thruster power. FIGS. 36-37 are top and side views of the vehicle showing the direction of force from the thruster. FIGS. 36-37 are top and side views of the vehicle showing the direction of force from the thruster. 38-39 are external and internal photographs of the submersible vehicle. 38-39 are external and internal photographs of the submersible vehicle. FIGS. 40-41 are photographs of a vehicle receiving a nose down pitching moment. FIGS. 40-41 are photographs of a vehicle receiving a nose down pitching moment. 42 and 43 are photographs of the vehicle including an angled control jet. 42 and 43 are photographs of the vehicle including an angled control jet. FIG. 44 is a vehicle trajectory graph for open and closed loop control.

  In light of the limitations of contact inspection vehicles, such as low speed and difficulty of control, we can operate in non-contact mode either within the structure and / or close to the surface of interest. Recognized benefits associated with possible vehicles. Such vehicles are faster and more reliable for applications such as various types of inspection without being disturbed by surface roughness, irregularities, or other variable characteristics of the surface or area being inspected Although cases may be provided, cases are also envisaged in which the vehicle disclosed herein is operated in contact mode. For example, such vehicles are not only for port security, but also for high speed such as inspection and maintenance of underwater infrastructure, pipelines, dams, oilfield drilling rigs and boiling water reactor internal systems, to name a few. Can be particularly beneficial in applications where accurate inspection can be advantageous. Although specific uses are noted above, the disclosed vehicles can be applied to any number of other uses.

  In order to enable non-contact control of the vehicle to the surface, the inventors have recognized the need to develop a vehicle geometry and control method to maintain a controlled clearance of the vehicle to the surface. While it may be possible to implement strict feedback control to adjust the gap in an underwater environment, such a brute force control method would likely require a powerful and extremely fast response actuator . Thus, in addition to any suitable feedback control loop used, we use the hydrodynamic effect between the vehicle and the inspection surface to automatically control the movement of the vehicle relative to the inspection surface. Recognized the benefits associated with that. That is, the inventors have used vehicle geometry that utilizes a so-called “ground effect” force that changes the fluid behavior close to the surface in order to control the vehicle in various ways as further detailed below. The shape and control method were developed.

  The term ground effect is used to describe the phenomenon that produces the force it incurs when the vehicle is close to the surface, but the phrase ground effect is due to the vehicle being close to the ground. It should be understood that this is not limited to situations where force is generated. Instead, the terms ground effect, ground effect power, or any related term include, but are not limited to, the ground, the seabed, the riverbed, the hull, the interior of pipes, and submerged structures (for example, Applicable to the operation of vehicles in close proximity to any surface, including dams and oilfield drilling rig supports.

  In some embodiments, ground effect forces applied to the vehicle in various ways can be manipulated to self-stabilize the vehicle at a desired distance relative to the surface. For example, the embodiments and examples described herein show that competing attractive and lift forces associated with ground effects, along with other forces applied to the vehicle, surface a stable net zero force or equilibrium position. FIG. 4 illustrates a method that can be balanced to produce one or more distances relative to. Due to the force change with distance to the surface at these stable equilibrium positions, as the vehicle is displaced away from the stable net zero force position, the net force changes and the vehicle is moved to a stable position. Energize to return toward. For example, in one embodiment, below a stable equilibrium position, lift begins to dominate, urging the vehicle upward away from the surface and toward the stable equilibrium position. Correspondingly, above the stable equilibrium position, the suction force begins to dominate and urges the vehicle downward to return to the surface and the stable equilibrium position. Thus, ground effect forces are utilized to implement self-stabilizing control methods that can be used in place of or in combination with other control methods to control the gap between the vehicle and the surface of interest. Can. In light of this effect, in some embodiments, the net force applied to the vehicle against the surface may decrease as the distance to the surface increases (ie, suction becomes more prevalent). Of course, the absolute value of this change in force with distance will depend on vehicle size, speed, applied thrust, gap distance, and desired application, to name a few. Thus, it should be understood that any suitable range of values for the desired application can be used.

  Although a negative change in net force vs. gap distance is noted above with respect to the stable equilibrium point above, the vehicle may be dynamic and / or static in areas where the change in net force vs. gap distance is positive. It should be understood that it can be operated on any of the following. Such an operation would simply not be self-stabilizing as described above.

  Various types of ground effect forces can be applied to the vehicle to help control the movement and positioning of the vehicle relative to the surface. Further, depending on the particular mode of operation, any one of these types of ground effect forces can be either alone or in combination with other types of ground effect forces as well as other forces acting on the vehicle. Used to control vehicle positioning and movement. Specific types of ground effect forces are described in further detail below.

  In one embodiment, the vehicle may generate ground effect forces due to the lateral movement of the vehicle relative to the surface. In such embodiments, without being bound by theory, lateral movement of the vehicle relative to the surface (ie, substantially parallel to the surface) causes the flow of fluid under the vehicle to affect the velocity of the vehicle through the fluid. Accelerate compared to. This can cause suction at the first distance and rebound from the surface at the second closer distance due to choking. In some embodiments, self-stabilizing equilibrium points may be located between these distances.

  In another embodiment, the vehicle may include one or more thrusters configured to be oriented toward the surface of interest. Depending on the diameter of the thruster, the applied thrust, and the distance from the surface, one or more jets can produce various ground effects. For example, a jet of fluid from a thruster can create a wall effect that creates a lateral flow of fluid between the vehicle and the surface, causing a low pressure area that sucks the vehicle toward the surface. The jet can also generate vortices, also known as the venturi effect, which also generate a suction force against the vehicle. In addition to the normal thrust from the thruster, there is also an upward force applied to the vehicle due to the observed fountain effect corresponding to the jet reflected from the surface towards the vehicle. The areas where these various effects predominate, and how they can be used together to control a vehicle, are described in further detail below.

  Although any suitably shaped and dimensioned vehicle can be used in conjunction with the described systems and methods, the inventors have recognized the benefits associated with using a particular vehicle shape. For example, in some embodiments, it may be desirable to reduce the stress applied to a vehicle under compression when the interior is not submerged. Thus, a smooth surface with a smooth curvature change can be used. In one example, a sphere can be used. However, the sphere can introduce control and stability problems. Thus, in another embodiment, an ellipsoid may be used, which is more suitable for movement using 5 degrees of freedom. In addition, shapes such as spheres and ellipsoids beneficially help maximize the volume to surface area ratio for a particular size vehicle. Ellipsoids mentioned include, but are not limited to, a ratio of major axis to minor axis that is between or equal to 1: 2, 1.4: 1.65, or any other suitable ratio. Can have any desired aspect ratio. In addition, an asymmetric ellipsoid may be used, where one half of the ellipsoid has a first aspect ratio and the other opposite half of the ellipsoid may have a different aspect ratio, which allows the vehicle to It can help to increase the ground effect suffered. While various arrangements of spheres and ellipsoids have been mentioned above, it should be understood that the vehicle may have any desired shape as the present disclosure is not limited to this scheme.

  Depending on the particular application, the vehicle may have any desired maximum outer dimensions. For example, in one embodiment, the vehicle has a maximum outer dimension that is between or equal to 5 inches to 60 inches, 24 inches to 48 inches, or any other suitable size range for the desired application. Can do. Thus, it should be understood that vehicles having outer dimensions that are both smaller and larger than those noted above are also envisioned, including large vehicles with dimensions of about a few tens of yards or feet.

  In addition to the overall shape of the vehicle, the inventors have recognized the addition of a flat portion on the vehicle body that can be oriented toward the surface of interest. In some embodiments, this flat portion of the vehicle body enhances the observed ground effect, enhances its stability as the vehicle moves through the fluid, and / or performs surface inspection to perform surface inspection. Can be sized and shaped to help position the sensor relative to. Depending on the particular embodiment, the flat part of the car body is 10% to 100%, 20% to 100%, 30% to 100%, 50% to the projected area of the car body oriented towards the flat part of the car body. It may have an area that is between or equal to 100%, 20% -80%, or any other suitable range of percentages. For example, a half ellipsoid shape corresponding to a flat body part having an area equal to the projected area of the associated ellipse part of the car body may provide a relatively large area for a sensor that may be useful in mapping applications. The vehicle maps its area with a larger number of sensors associated with the flat part of the car body as it is moved relative to the sea floor using ground effect forces.

  It should be understood that the vehicle body and various other components described herein can be made from any suitable material. For example, the car body can be made from various metals, polymers, ceramics, and / or combinations of these materials. In addition, in some embodiments, the flat portion of the vehicle body intended to be oriented toward the surface of interest is an elastic material such as an elastomer (eg, rubber, polyisoprene, polybutadiene, polyisobutylene, polyurethane, etc.) Can be made from While not being bound by theory, such a surface can help smooth the response of the vehicle as it traverses a surface containing irregularities in either contact and / or standoff mode.

  A vehicle capable of maintaining a distance to a surface may be applicable in some applications, but such a vehicle is used when performing various types of inspection and / or maintenance. It can be particularly beneficial. For example, as noted above, in some embodiments, the vehicle may include one or more for sensing information about the surface, such as the hull, the bottom of the seabed, or any other object or location of interest. May include more sensors. Suitable types of sensors that can be used include, but are not limited to, ultrasonic sensors, eddy current detectors, magnetic sensors, cameras, optical sensors, temperature sensors, pressure sensors, PH sensors, turbidity sensors, oxygen sensors, carbon dioxide Includes sensors, linear sensor arrays, phased sensor arrays, and any other suitable type and / or arrangement of sensors.

In some embodiments, depending on the type of sensor used, the sensor may have a desired sensing range that is desirable to maintain the sensor therein when sensing information from the surface. In one such embodiment, a sensor, such as an ultrasonic sensor, has a preferred sensing range that is related to the wavelength of the ultrasonic wave. Specifically, when the sensor is placed at an odd multiple of a quarter wavelength away from the surface, the overlapping waves are summed in-phase at the transducer to produce a signal maximum. In contrast, when the sensor is placed at an even multiple of a quarter wavelength, the waves cancel each other and the signal is at its minimum. Thus, in some embodiments, the sensing range for an ultrasonic sensor may be an odd multiple of a quarter wavelength ± 0.5. In one such embodiment, a 300 KHz ultrasonic transducer has a wavelength of 4 mm in water (c _w = 1,500 m / sec), which is converted to a quarter wavelength of 1 mm. Therefore, the maximum signal is obtained at 1 × n mm from the surface, where n is an odd number.

  Based on the foregoing concept, in one embodiment, a vehicle immersed in fluid may be controlled, at least in part, by positioning the vehicle at a preselected distance relative to a surface such as a hull or seabed. In some cases, the preselected distance may correspond to a stable equilibrium distance of the vehicle relative to the surface. Once properly positioned, one or more ground effect forces are applied to the vehicle, generating a net zero force that is applied to the vehicle at a preselected distance to the surface of interest. One preselected distance may be maintained. For example, various types of ground effect applied to the vehicle, the net weight of the vehicle (ie, actual weight minus buoyancy) applied to the vehicle from a source such as an associated thruster With force, there can be a total of zero in the direction oriented towards the surface. As the vehicle is displaced away from the preselected distance relative to the surface, the ground effect force changes and automatically urges the vehicle back toward the desired preselected distance relative to the surface. obtain. As described in more detail below, ground effect forces can be generated using lateral movement of the vehicle relative to the surface, jets impinging on the surface, and / or a combination of both.

  Turning now to the figures, some non-limiting embodiments are described in further detail. However, although specific embodiments are described, the various features and concepts described below are not limited to those embodiments described herein, and thus are in any suitable combination. It should be understood that it can be used.

  1A-2C depict various schematic views of an embodiment of a vehicle 2 that can be submerged in a fluid such as water. The vehicle includes a vehicle body including a first portion 4 and a second flat portion 6. As illustrated in the figure, the first portion of the vehicle body may be a gently curved structure, such as a partial ellipsoid, a sphere, or other suitable shape with a flat portion that forms a flat bottom surface of the vehicle. . However, since the present disclosure is not so limited, shapes that include shapes and features that are not gently curved are also envisioned. In addition, depending on the particular application and / or design criteria, the flat portion of the vehicle body may have an area that is any suitable percentage of the projected area of the corresponding portion of the body.

  In order to control the steering of the vehicle, in some embodiments, a plurality of thrusters 8 are distributed around the first portion of the vehicle body 4. These thrusters can be oriented in any number of desired ways to provide thrust in various directions. For example, the thruster may be positioned and oriented to provide thrust in a direction oriented vertically downward and / or laterally relative to the flat bottom portion 6 of the vehicle. Of course, thrusters oriented at angles that provide both vertical and lateral thrust components to the vehicle are also envisioned. Further, in some cases, these thrusters may apply their thrust to the vehicle along an axis that passes through the vehicle's center of gravity. Without being bound by theory, this can help eliminate or reduce undesirable moments applied to the vehicle during maneuvering.

  In addition to the thrusters located on the elliptical portion of the vehicle body noted above, in some embodiments, one or more thrusters are also associated with the flat portion 6 of the vehicle body and the flat bottom portion of the vehicle body. Can provide thrust directed upwards. For example, the central thruster 10 may be positioned approximately at the center of the flat portion and may apply a thrust that is oriented perpendicular to the flat surface. In addition, the plurality of thrusters 12 can be similarly distributed around the flat portion of the vehicle. In some instances, the plurality of thrusters are evenly distributed around the flat portion of the vehicle and / or around the periphery of the flat portion. As depicted in the figure, in one such embodiment, the plurality of thrusters includes two or more thrusters located on opposite sides of the central thruster. While not being bound by theory, this can help balance the thrust applied to the vehicle during operation. However, embodiments in which the thrusters are arranged in a non-uniform manner or elsewhere are also envisioned. Further, as will be described in more detail below, the thrusters associated with the flat bottom car body portion are oriented vertically or angled with respect to the car body flat portion, depending on the desired vehicle control. It can be either.

  For clarity, the thrusters noted in the above description and illustrated in the figures correspond to thruster exits. However, the depicted structure may correspond to either a thruster outlet or an inlet, which again understands that the present disclosure is not so limited and can be placed on any suitable part of the vehicle I want to be. For example, in one embodiment, the vehicle may include a plurality of thruster outlets disposed on the top, bottom, front, and rear of the vehicle relative to the main direction of travel. Correspondingly, one or more associated thruster inlets can be arranged on the side of the vehicle. However, it should be noted that other locations for both the thruster inlet and outlet are also envisioned. Further, in cases where the interior of the vehicle is flooded during use, the vehicle may or may not include any thruster inlet formed outside the vehicle.

  In the embodiments described herein, a thruster may refer to any suitable device that can apply thrust to the vehicle to control the movement of the vehicle. Suitable types of thrusters include, but are not limited to, pressure jets, steering jets, tunnel thrusters, and propellers, to name a few. In cases where a jet or other similar device is used, any suitable hydraulic power source can be used to power the jet, including rotary pumps, centrifugal pumps, gear pumps, reciprocating pumps, turbines, and any A number of other types of devices may be included. In cases where it may be desirable to provide a relatively constant or more controlled thrust, a pressure reservoir such as an accumulator may be connected between the hydraulic source and the outlet from the jet. In addition, individual valves and / or power supplies may be associated with each thruster to provide individual and / or grouped control of the thrusters. However, in some embodiments, one or more pressure distribution systems may be used to fluidly couple a pressure source with multiple thrusters, which reduces vehicle size and complexity. Can be helpful.

  As previously mentioned, the vehicle may include one or more sensors. In addition, the flat body part may be a particularly useful place for positioning sensors for sensing information from the surface of interest. For example, a flat surface provides a larger area for placing various sensors for inspecting the surface, allowing the use of larger sensors, sensor arrays, and / or a greater number of sensors. As shown in FIGS. 1C and 2C, the individual sensors 14a may be distributed around a flat portion of the vehicle body. Alternatively, or in addition to a plurality of individual sensors, the vehicle may also include an array 14b of sensors. In the depicted embodiment, the array of sensors extends at least partially across the width of the flat body portion. This increased area and / or length in which the sensor is located is scanned by the sensor during a single pass when inspecting the sensor's detectable threshold, sensed signal fidelity, and / or surface. The area that can be increased. In the depicted embodiment, the sensor array extends in a direction that is generally perpendicular to the main direction of travel of the vehicle, but embodiments in which the array extends in a direction that is generally parallel to the main direction of travel of the vehicle are also possible. Also envisioned. In addition to the larger area for housing the sensor, the use of a flat body part allows two or more sensors and / or transmitters and associated receivers to be in the same plane when inspecting the surface. Make it possible to do. In various applications, including, but not limited to, triangulating the distance to a particular feature on the surface using three distance sensors located in the same plane corresponding to the flat body part Can be beneficial.

FIGS. 3-5 show a bottom view and a side view of the vehicle body including a first portion 4 having a partially elliptical shape and an associated second flat portion 6. The partial elliptical part of the car body has principal radii a ₁ , b ₁ and c ₁ . As can be seen in the figure, the flat body part corresponds to the place where a part of the ellipsoid has been removed, producing a flat ellipsoid with principal radii a ₂ and b ₂ . As illustrated by FIGS. 4 and 5, the flat portion of the vehicle body may be located either above or below the elliptical center plane parallel to the flat vehicle body portion. Thus, depending on the particular embodiment, the distance c ₂ from the flat body part to the opposing vertex of the oval shape may be less than, greater than or equal to the principle radius c ₁ of the partial oval shape. Correspondingly, the area of the flat part, which is πa ₂ b ₂ in FIG. 4, may be less than or equal to the projected area of the first part of the car body oriented towards the flat car body part, Again, FIG. 4 corresponds to πa ₁ b ₁ . However, as shown in FIG. 5, when the flat portion of the vehicle body is located at or above the center plane of the partially elliptical shape, the projected area of the first portion of the vehicle body is equal to the area of the flat vehicle body portion. Therefore, in addition to the area relationship noted above, the distance between the opposite side of the first portion of the vehicle body and the flat vehicle body portion (ie, c ₂ ) corresponds to the first portion of the vehicle body. Between 10% to 80%, 10% to 70%, 10% to 60%, 10% to 50%, or any other suitable percentage of the corresponding width of the ellipsoid (ie 2c ₁ ), Or they can be equal. Although the areas and distances noted above are related to elliptical shapes, these concepts can be applied to any other suitable shape, as the disclosure is not so limited.

  6 and 7 illustrate the vehicle 2 traversing the surface in a lateral direction that is generally parallel to opposing portions of the surface 100 located directly below the vehicle. The vehicle is traversed over the surface at some desired speed V. As depicted in the figure, the surface may include any number of irregularities 102, such as protrusions, objects, weld seams, and other possible features associated with that particular surface. Alternatively, the surface that the vehicle is traversing to the side can be curved as expected for the hull, as shown in FIG. In such an embodiment, the vehicle may be considered to move laterally, i.e., substantially parallel to the curved portion of the vehicle body facing the vehicle, and continue a non-linear path according to the curvature of the surface it traverses. obtain. In any case, these variations in surface location and / or irregularities located on the surface affect the distance h between the bottom surface of the vehicle and the surface of interest that the vehicle crosses laterally. Further, in some applications, such as when a sensor is used to sense information to a surface, when these changes in surface location and / or irregularities are encountered, the bottom surface of the vehicle and the surface being inspected It may be desirable to control this distance between the sensors to ensure that the sensor can properly sense information from the surface. Various strategies and vehicle configurations for controlling this distance are described in further detail below.

  In the embodiment depicted in FIGS. 6 and 7, the vehicle 2 does not include a tether, which often reduces the chance of the vehicle getting tangled in a crowded environment, such as that encountered during inspection. Can help to make it. In addition, the lack of tethers can also result in easier vehicle handling and faster vehicle scanning speeds against rough or irregular surfaces compared to conventional tethered vehicles in contact with the inspection surface. . However, embodiments where a moored vehicle is used are also envisaged.

  As noted above, lateral movement of the vehicle relative to the surface is a possible way to generate ground forces. Furthermore, the balance of ground forces applied to the vehicle is related to the distance h between the vehicle and the ground. For example, without being bound by theory, the fluid force on the vehicle due to the presence of the surface depends on the specific gap ratio ε = h / c, where h is from the surface of interest to the vehicle bottom. Distance. C is the chord length of the main body. Typically, an ε value equal to about 0.1 results in a suction (venturi) force, which is often used in race cars to increase the downward force experienced. However, for ε values below 0.08, it is found that the boundary layers merge and instead lift occurs, providing what is known as a wing in the ground effect, which increases the lift experienced. Moreover, it is used in some vehicles. However, with respect to self-stabilization, instead of a constant downward or upward (WIG) force, in some embodiments, the target biases the vehicle back toward the desired position relative to the surface. It is to generate a net zero force region with a gradient.

  8A-9B illustrate a simplified two-dimensional model of a partially elliptical vehicle 2 in which the flat bottom portion 6 of the vehicle body travels laterally with respect to the surface at a speed U. As noted above, depending on the height of the vehicle relative to the surface 100, different flow forms are encountered. For example, without being bound by theory, for a region that is very close to the surface, the vehicle suffers a significant viscous effect, and the flow in this region is most effectively understood through boundary layer interactions. For areas close to the surface but above the boundary layer thickness, there is a flow path between the body and the surface. The flow in this region is determined by a combination of Bernoulli effect and Couette flow. Thus, the increased velocity in this channel results in a lower pressure (ie suction), called the venturi effect. In addition, for regions farther from the surface where the ground effect is less noticeable, the flow transitions to an unrestricted medium and the ground effect force, if present, can be completely ignored. These various regions and the resulting forces are further described below. Although the regions are described as being discrete from each other, various attractive forces and lifts exist in each region in variable amounts, which types of forces predominate in that particular region, and to what extent It should be understood that whether force dominates the observed vehicle behavior becomes more problematic.

When the vehicle body is in close proximity to the surface, the lift experienced can be explained through many theories. For example, for gap sizes with ε equal to or less than 0.01, well-known lubrication theories can be used that address the interaction of the boundary layer as the two surfaces move in relative motion. it can. The flow here is very viscous and a reduced Reynolds number is given by ε ² Re. For simplicity, a small area directly above the base of the vehicle is modeled as a variable height tilt slider that is moved relative to the surface at a constant speed U, as shown schematically in FIGS. 9A and 9B. Can be The fluid has a velocity of v _{x that} varies with the z position relative to the bottom surface of the vehicle. The governing equations for determining the resulting fluid velocity and pressure are the 2D Naviestokes equation for incompressible flow and the Reynolds equation for lubrication theory. Qualitatively, the fluid enters the inlet pressure P _i at point A with a height of h _i . As the fluid flow passes through the A to B wedge, which represents an idealized shape that can cause the observed effect, a maximum pressure P _o occurs at point h _{o at} point B. However, it should be noted that the rebound and / or lift observed by the vehicle can also be attributed largely to the choking effect observed in the gap. The pressure then undergoes a linear drop in pressure from points B to C, which can be modeled as a parallel plate with an expected linear drop in pressure between these points. Schematic model, then, is another idealized geometries which may cause behavior observed, through the wedge segments to expand from C to D, therefore, return the pressure to P _i. The pressure at any point of the body, ambient pressure (i.e., the inlet pressure) for greater than or, as shown in FIG. 8B, positive lift F _L of the net, acting on the vehicle. This phenomenon can also be understood as arising from the interaction between the two boundary layers that can merge and cause choking in the channel, resulting in observed lift. In addition to increased lift, the vehicle can also experience increased drag due to viscous friction between the boundary layers moving relative to each other.

In the region above the combined thickness of the boundary layer, where the flow is non-viscous but can still be considered to exist with a slight gap from the surface, the flow is as shown in FIGS. 9A and 9B: In order to better understand the observed phenomenon, it can be modeled as a fluid entering an idealized geometry pipe with a narrowed diameter. Radius, begin with _{h i,} reduced to _{h o,} then, to expand so as to return to _{h i.} From the Bernoulli equation, this causes a corresponding increase in velocity in a narrow section, resulting in a reduced pressure or suction force Fv, which can be modeled using the Bernoulli equation. The boundary layer enhances this effect as the moving ground draws fluid into the gap (ie, Couette flow).

The lift and suction (i.e., venturi) forces noted above are opposite to each other and vary in strength as the gap is varied, and lift attenuates faster than the venturi force as the gap distance increases. Between a smaller distance that suffers net lift and a larger distance that suffers net attraction, there is an equilibrium point where the force in the vertical z direction acting on the vehicle is net zero. In other words, F _L is equal to F _v, the vehicle there is a point to be assumed to be floating in neutral. For example, as described in more detail in this example, the value of ε is positive using the following region shown in FIGS. 20 and 21, ie, lateral movement of the vehicle, using ε = h / c. Region a corresponding to ε ≦ 0.01, where negative lift (ie suction force) occurs from lateral movement of the vehicle, region b corresponding to 0.01 ≦ ε ≦ 0.3, net A zero ground effect force occurs at about ε = 0.01, between regions a and b, and a region c corresponding to ε ≦ 0.3, where the ground effect force is no longer significant. The overall magnitude of the ground effect force can also increase as vehicle speed increases. In addition to the above, a negative slope of lift versus gap distance can exist for various values of ε. In addition, any number of different ratios can cause negative slopes due to lateral movement of the vehicle relative to the surface due to effects from changes in size, shape, speed, and flow morphology, to name a few. It should be understood that it may be possible to provide. As noted above, this response in force versus gap distance can be utilized to generate one or more stable equilibrium positions of the vehicle relative to the surface. Of course, since the present disclosure is not so limited, vehicles operating at stable equilibrium points outside the noted ε range due to the use of other types of ground effect forces are also envisioned.

  In light of the above, the vehicle can be operated at a distance relative to the surface to generate ground forces due to the lateral movement of the vehicle relative to the surface with any number of different values of ε. However, in one embodiment, the vehicle may be operated at a value of ε below or equal to about 0.3, 0.1, 0.05, 0.01, or any other suitable value. Correspondingly, the vehicle may be operated at a value of ε above or equal to about 0.001, 0.005, 0.01, 0, 05, or any other suitable value. Combinations of the above are envisioned including, but not limited to, about 0.001-0.3 or equivalent. Of course, the operation of vehicles in different ranges, both larger and smaller than noted above, in particular uses different sized vehicles, operates at different speeds and / or differs. Assumed when using a form of ground effect.

  Without being bound by theory, the magnitude of the ground effect force generated using the lateral movement of the vehicle relative to the surface increases as the vehicle speed increases. Thus, increasing the speed of the vehicle will increase the lift applied to the vehicle and / or the applied suction. Thus, the speed of the vehicle can be controlled to balance one or more other forces acting on the vehicle, or the speed can be toward or away from the surface producing the noted ground effect force. It can either be controlled to urge the vehicle in a desired direction. In addition to the above, when the vehicle is located in a region where the change in ground effect force with respect to the gap distance is negative, altering the vehicle speed can also cause the vehicle to have a stable equilibrium position relative to the surface from the first position. It can be changed to the second position.

  In one embodiment, the control parameters for the vehicle noted above may be combined with a vehicle that includes a surface such as a flat body portion. In addition, the surface may include one or more sensors with a desired sensing range as noted above. The flat body part has an appropriate chord length and a sufficient amount of thrust in the desired scanning or movement direction, and is at least within the desired sensing range of the sensor when the vehicle is moved laterally relative to the surface. One stable balanced ground effect height can be generated. Of course, embodiments in which the chord length and thrust capacity are selected to provide a stable balanced position at other desired positions relative to the surface are also envisioned.

  In another embodiment, a method for controlling the positioning of a vehicle using ground effect forces is directed to the vehicle using one or more jets that are directed toward a surface of interest in which the vehicle is located in close proximity. Generating a ground effect force. As will be described in more detail below, although not bound by theory, the ground effect force associated with one or more jets impinging on the surface is a combination of traditional lubrication theories in small gaps. is there. However, as the distance to the ground is increased, lift loss (i.e. suction) induced on the ground begins to prevail, which pulls the vehicle back towards a smaller gap. Therefore, there is a stable equilibrium point for the jet from a small distance to an intermediate distance. As the clearance is further increased, the lift enhancement from the blowup pushes the vehicle away until the thrust applied to the vehicle is equal to that in free flow, which also separates the vehicle from the ground. Can be used to generate a stable equilibrium point. These individual phenomena are further explained below with reference to the figures.

  FIG. 10A illustrates one embodiment of the vehicle 2 that includes an inlet 18 in fluid communication with a pressure source 16 such as a centrifuge or other suitable type of pump or turbine. The pressure source, in some embodiments, includes communication with the central thruster 10 located in the center of the flat portion of the vehicle body. In particular, the thrusters are oriented vertically downward with respect to the flat body part. In addition to the vehicle's net weight W (actual weight minus buoyancy), an upward thrust T applied to the vehicle is provided. The vehicle is depicted as being removed from any associated surface and therefore does not include any ground effects that affect it.

  FIG. 11A illustrates a vehicle located within a surface distance h. Depending on the specific distance and sizing of the thruster 10, different types of ground effect forces can prevail at different intervals. As shown, the jet flow from thruster 10 toward surface 100 produces three different regions of interest that are dominated by three different types of fluid flow. Two parameters that serve to characterize which particular type of fluid flow and the resulting ground effect force predominate are the specific gap lengths ε = h, as detailed above for lateral movement. / C, where h is the gap height and c is the specific body length or associated surface chord length. Another parameter is the ratio of the distance h to the ground relative to the thruster diameter d, which is given by η = h / d. The different areas of interest shown in the figure are further described below.

Initially, in the first region, the thruster 10 is turned on when the bottom surface of the vehicle, such as the flat bottom body portion 6, contacts the surface 100. Upon contact, the flow will attempt to exit, but cannot exit due to the surface blocking the flow from the thruster. At a particular pressure for a given opening size, the pressure produces a lift L _f that is large enough to raise the body by a minimum distance sufficient to relieve the pressure (see region 1 in FIG. 31). . A thin film is then generated directly under the vehicle. This is somewhat similar to radial flow through air bearing sliders or parallel disks, and the body is 0.5 mm to 4 mm, 1 mm to 2 mm, or any other suitable fluid film thickness, or It remains in a stable equilibrium distance with respect to the surface on the thin film of low velocity fluid having a thickness equal to. Furthermore, fluid films having both greater and lesser thickness than noted above are also envisioned depending on thruster strength and sizing and vehicle size. This phenomenon is commonly referred to as the lubrication theory for fluid film formation and is not constrained by theory, but this explanation is that the flow can be approximated as a low Reynolds number laminar flow and the inertial force is greater than the viscous stress. As long as it is small, it is effective.

When the gap distance h is increased to the second area (see area 2 in FIG. 31), the vehicle suffers a sudden loss of lift, i.e., the change in lift with increasing gap distance is negative. Without being bound by theory, this is due to the fact that the jet from thruster 10 impinging on surface 100 flows parallel to the surface and, together with the radiating wall jet, creates a low pressure region under the vehicle. To do. This low pressure region provides a strong suction force L _S. This suction effect depends on the ratio η = h / d between the proximity to the ground and the nozzle diameter and the nozzle pressure ratio (NPR), which is the ratio between jet stagnation pressure and ambient pressure. Thus, in close proximity to the surface, it can be expected that the presence of the ground will provide additional lift while at the same time suffering a strong suction force or negative pressure region at small distances above the fluid film distance. . For example, for η ≦ 0.3, the flow radiating from the vehicle remains attached to the body at the leading edge, resulting in a small ground vortex in the gap, which results in a negative pressure that decreases with increasing height. You can see that The suction force at η ≧ 0.3 also causes the main jet to take up the fluid directly under the vehicle body along with the wall jet, thereby accelerating the water directly under the vehicle and between the upper and lower sides of the vehicle. It can also be understood from the fact that it creates a negative pressure difference, which causes a sudden reduction in the low pressure area under the vehicle and the corresponding lift. However, as the height is increased relative to the ground, the vortex disappears and the pressure differential goes to zero.
region

  In addition to η and NPR noted above, other parameters that are said to affect the induced lift (positive or negative) are the jet structure and the jet impact angle to the ground.

For larger gap distances h corresponding to the third region, the suction force is reduced and the fountain blast from the jet impinging on the surface begins to dominate the ground force (see region 3 in FIG. 31). Specifically, the jet that collides with the surface is reflected upward from the ground toward the bottom of the vehicle. This effect, generally referred to as the fountain effect, produces a positive pressure on the underside of the vehicle, which increases the lift L _f acting on the bottom part of the vehicle's car body oriented towards the surface. However, the fountain effect is suppressed relatively rapidly when the vehicle is brought closer to the ground due to the strong suction force. In addition, the fountain effect eventually decays to zero when the gap is increased, resulting in free flow thrust applied to the vehicle at larger gap distances. Note that the fountain effect is observed for both single and multiple jets impinging on the surface. In addition, it should be noted that the fountain effect may not overcome the suction force for slower jets, as illustrated in the examples below. Thus, the presence of positive lift in this third region has sufficient thrust capacity to produce a fountain effect that is large enough to overcome the associated suction effect that predominates the ground effect force in region 2. A thruster can be a condition.

  In light of the above, in one embodiment, region 1 corresponding to pressure build-up and thin fluid film may exhibit η between 0.08 and 0.6, or region 2 corresponding to suction is 0.6. The region 3 corresponding to the fountain blast can exhibit η of 64 to 200 or equal to them. Of course, it is expected that region 3 may extend to η above or equal to 32 in some cases. Corresponding stable equilibrium points were observed at about 1 mm, 100 mm, and 500 mm. Again, the values determined above are for a particular vehicle, and values above and below what is noted above for each region are also different vehicle sizes, thruster speeds, designs, and operating parameters. It should be understood that this can occur due to the η values associated with these regions varying with respect to.

FIG. 11B shows the various forces acting on the vehicle when the jet is directed towards the adjacent surface. As shown in the figure, the vehicle has a net weight W (actual weight minus buoyancy), a suction force L _s acting downward on the vehicle toward the surface, and a flat bottom body portion 6. It includes a thrust T oriented upward and a lift L _f from the noted fountain effect. Also, as seen in FIG. 31a, the combined force-to-gap size including thrust applied to the vehicle and ground effect force, ie, the slope of the distance from the corresponding surface, is the force-to-gap distance at the two locations. , Indicating that there are two stable equilibrium positions for the vehicle relative to the surface. First, for small gaps (ie, small η), the suction and the net weight of the vehicle can be balanced against the thrust and lift of the vehicle to keep the vehicle in a balanced position. In a second stable equilibrium position that is approximately the size of the vehicle or larger, the net weight of the vehicle is balanced against the thrust by adding fountain blowing and subtracting the weakened suction force. . Like the above, in both a stable balanced position of the upward perturbation gap distance, while reducing the contribution of lift L _f, downward perturbation gap distance increases the lift L _f. Thus, the ground force changes as the distance changes and automatically biases the vehicle toward the desired equilibrium position. However, the specific distance at which this condition occurs depends on the thruster, or jet, velocity. Thus, the thruster speed can be increased or decreased to correspondingly increase or decrease the gap distance of each second stable equilibrium position. However, a second equilibrium position located at a larger gap size (ie, a larger η) has a smaller slope and therefore has a greater variation in the equilibrium position than an equilibrium position located closer to the surface. Note that it allows. In addition, for a sufficiently low speed, the second stable condition can disappear due to the fountain effect being overcome by the suction effect.

  As noted above, in addition to the thruster diameter interaction, in some embodiments, the ratio ε = h / c may also affect the equilibrium distance experienced by the vehicle. For example, the stable equilibrium distance can vary based on speed, thrust, vehicle size, and shape, to name a few, but these ground effect forces are about 0.5-1.5 from the surface. May result in a lower stable equilibrium position with an ε value corresponding to a body length of 5 and a higher stable equilibrium position with an ε value corresponding to a body length of about 4-10. However, again, different values for these ranges, both larger and smaller, are also envisaged due to changes in vehicle design and / or operation.

  Two separate methods for generating and controlling various types of ground effect forces have been described above, but these methods may be used separately or in combination as the present disclosure is not so limited. It should be understood that either can be used. For example, one or more stable equilibrium positions with respect to the vehicle relative to the surface may cause the net weight of the vehicle immersed in the fluid to a net thrust (thrust direction and / or magnitude) applied to the vehicle away from the surface. Resulting in one or more thrusters oriented towards the surface producing the suction and / or fountain blasts, and / or lateral movement of the vehicle relative to the surface, and / or Can be generated by balancing with ground effect forces. In addition, the speed of the vehicle relative to the surface, the magnitude of the thrust, and / or the buoyancy of the vehicle may be altered to alter the resulting stable equilibrium position of the vehicle.

  In light of the above, various embodiments of a vehicle may include thrusters oriented in various directions at any number of locations. For example, FIGS. 12A and 12B illustrate one embodiment of a vehicle that includes a thruster oriented upward away from the flat bottom portion 6 of the vehicle body. The vehicle also includes one or more laterally oriented thrusters 8b and 8c that apply thrust to the vehicle in a direction parallel to the flat bottom portion of the vehicle body, but at an angled side. A thrust can also be applied. A central thruster 10 and two thrusters 12 located on opposite sides of the central thruster are oriented vertically downward with respect to the flat bottom portion of the vehicle body. Pressure is applied to these thrusters using a suitable pressure source 16 that is fluidly connected to an unillustrated inlet. The pressure source is in electrical communication with the controller 20, which controls the operation of the pressure source and various associated thrusters.

  13A and 13B illustrate an alternative embodiment of the vehicle 2 that includes a thruster located on the flat bottom portion 6 of the vehicle body that is located radially outward with respect to the central thruster 10. In this embodiment, the thruster surrounding the central thruster is angled downward and laterally away from an axis that passes vertically through the center of the flat bottom portion of the vehicle body. Such a configuration can help the lateral stability of the vehicle relative to the surface. In yet another alternative embodiment (see FIGS. 14A and 14B), a thruster located radially outward from the central thruster 10 on the flat bottom portion of the vehicle body passes vertically through the center of the flat bottom portion of the vehicle body. Enhances the fountain effect resulting from thrusters that are angled downward and inward toward the axis and impact the surface. In some embodiments, one or more of the thrusters oriented downwardly and laterally inwardly on a flat portion of the vehicle body, and in some cases, all of them towards point 20. Oriented.

  Although simple pumps connected to various thrusters are illustrated in the above figures, the pressure source 16 is not limited to this disclosure, so the pump, turbine, propeller, accumulator, valve, distribution manifold, and It should be understood that any suitable combination of / or other suitable hydraulic components may be accommodated.

  As illustrated in FIGS. 15-18, sometimes the surface 100 on which the vehicle 2 is located adjacent is arranged in an orientation other than vertically upward, as may occur during any number of inspection processes. For example, in addition to being oriented vertically upwards as can be expected with respect to the sea floor, the surface is oriented vertically downwards and / or at any angle therebetween, as can be expected with respect to the bottom of the hull. Can be done. Thus, in some embodiments, a vehicle that includes a flat bottom portion of a vehicle body may be able to be oriented in any desired orientation to align the flat portion of the vehicle body 6 with a corresponding surface of interest. . The ability to orient the vehicle can be accomplished in any suitable manner. However, in one embodiment, the vehicle is oriented by adjusting the position of the center of gravity of the vehicle. This variable center of gravity may be provided in any number of ways, including but not limited to a displaceable weight or ballast located inside the vehicle. Alternatively, the buoyancy in the vehicle can be modified to control the vehicle orientation. This may be any suitable, including but not limited to the use of one or more selectively inflatable bladders located in various locations within a submerged vehicle or in a selectively submersible compartment. Can be carried out in style.

  In the above embodiment, the vehicle may initially be oriented towards the surface of interest. If it is desired to maintain the vehicle's position relative to the surface in that orientation, then the vehicle is moved laterally relative to the surface and / or the thrust is directed towards the surface On the other hand, a corresponding thrust is applied to the vehicle to urge the vehicle toward the surface of interest. Correspondingly, a substantially zero force can be applied to the vehicle in a direction oriented toward the surface to produce a stable balanced position at the desired location. For example, the net weight of the vehicle, the thrust both toward and away from the surface, and the sum of the corresponding ground effects can be balanced in the direction oriented toward the surface. Of course, the ground effect force applied to the vehicle includes components from moving the vehicle laterally relative to the surface and / or applying a thrust directed toward the surface. In addition, the resulting change in force aligned with the surface with increasing gap size is negative and may ensure that the vehicle is biased toward the desired location when the distance is modified. However, an operating mode in which the change in force versus gap size is positive is also envisioned.

  Having described various control methods and vehicle configurations, one embodiment of a method for controlling a vehicle relative to a surface is described in connection with FIG. In this figure, at 200, the vehicle is steered, oriented and / or otherwise positioned at a first preselected distance relative to the surface. At 202, the vehicle is then moved laterally relative to the surface and / or thrust is applied toward the surface, subsequently affecting one or more of the vehicle dynamics. Generate ground effect power. At 204, the thrust applied to the vehicle in which the net weight of the vehicle (i.e., the vehicle weight minus buoyancy) is oriented toward and / or away from the surface with the resulting ground effect force. Is balanced. As noted above, the distance at which the net zero force applied to the vehicle oriented towards the surface occurs can be a stable equilibrium point. Furthermore, in some embodiments, the preselected distance to the surface corresponds to a stable equilibrium position, which, as noted above, is the vehicle shape, the vehicle's lateral velocity relative to the surface, the thruster diameter. , And the magnitude of the jet impinging on the surface from a thruster oriented towards the surface.

  Once properly positioned with respect to the surface, a control loop is implemented. At 206, one or more sensors sense the distance between the bottom surface of the vehicle and the surface being inspected. If the vehicle is within a threshold distance from the first preselected distance relative to the surface, various parameters related to ground effect forces are maintained at 208 and 212, which can be used to reduce existing hydrodynamic forces. Used to provide automatic control of the vehicle centered on a stable equilibrium position. However, if the vehicle is outside the desired threshold distance from a preselected distance relative to the surface, the thrust applied to the vehicle relative to the surface and / or the lateral speed and / or thrust directed towards the surface One or more parameters controlling the ground effect force, such as the magnitude of, may be modified at 210. These modified forces then urge the vehicle toward the desired first preselected distance against the surface. The appropriate threshold distance will depend on the particular application. However, in some embodiments, an appropriate threshold distance may be based on an absolute distance threshold or a threshold based on the size of the vehicle and the application to which it is applied. For example, the threshold can be selected to maintain the sensor within a desired sensing range.

  In some cases, it may be desirable to move the vehicle to a different second preselected distance relative to the surface, as may be the case at 214 using different sensors with different desired sensing ranges. possible. If such adjustment is desired, at 216, the thrust applied to the vehicle relative to the surface and / or the associated ground effect force is controlled to move the vehicle to a second preselected distance. Again, this can again correspond to a stable equilibrium position, but the case is also envisaged where this second position is simply controlled using a feedback loop. For example, in one embodiment, the applied thrust, which is directed towards the surface, is modified from a stable equilibrium point closer to the surface, which may be suitable for proximity range sensors, It may be desirable to move towards a more remote and stable equilibrium point, which is more appropriate for visual inspection of surfaces using other wider range sensors. In any case, at 218, once the vehicle is within the desired sensing range, one or more sensors may sense information associated with the surface. If the surface inspection is not complete at 220, the control loop continues. Alternatively, once the inspection is complete, the vehicle can be steered away from the surface and controlled in any other suitable manner (see 202).

  In addition to modifying the various thrust and ground effect forces associated with the vehicle, in some embodiments, the net weight of the vehicle in the fluid is also modified to assist in controlling the position of the vehicle. obtain. For example, the vehicle has variable buoyancy provided by one or more inflatable bladders, fillable chambers, and / or any other suitable arrangement capable of varying the buoyancy of the vehicle in fluid. Can have.

  The above-described embodiments of a system including various control methods and a controller for implementing those methods may be configured in any number of ways. For example, a controller may correspond to any suitable computing device, which may be memory and whether provided within a single computing device or distributed among multiple computing devices. It can be configured as any suitable processor or collection of processors associated with it. Such a processor is one or more of the integrated circuit components, including commercially available integrated circuit components known in the art by names such as CPU chip, GPU chip, microprocessor, microcontroller, or coprocessor. It can be implemented as an integrated circuit with more processors. Alternatively, the processor may be implemented in a custom circuit such as an ASIC or a semi-custom circuit resulting from configuring a programmable logic device. As yet a further alternative, the processor may be part of a larger circuit or semiconductor device, whether commercially available, semi-custom, or custom. As a specific example, some commercially available microprocessors have multiple cores, and thus one or a subset of those cores may constitute the processor. However, the processor may be implemented using circuitry in any suitable format. Further, the computing device includes, but is not limited to, a rack mount computer, desktop computer, laptop computer, tablet computer, smartphone, separate custom designed control device, or any other suitable computing device. It should be understood that the invention may be embodied in any of several forms, such as a computing device connected to a vehicle through a tether or wirelessly. In addition, the computing device may be integrated directly with the vehicle, in which case the vehicle may be autonomous and / or receive and execute commands received either wirelessly or through a tether. Can be configured as follows.

  Also, the various methods or processes outlined herein may be encoded as software executable on one or more processors employing any one of a variety of operating systems or platforms. obtain. In addition, such software can be written using any of a number of suitable programming languages and / or programming or scripting tools, and can be executed on a framework or virtual machine. It can be compiled as language code or intermediate code.

  In this regard, the disclosed embodiments are computer-readable storage media that, when executed on a vehicle, are encoded using one or more programs that implement the various methods and processes discussed above. (Or multiple computer-readable media) (eg, computer memory, one or more floppy disks, compact disks (CDs), optical disks, digital video disks (DVDs), magnetic tapes, flash memories, field programmable gate arrays or It may be embodied as a circuit configuration in another semiconductor device, or other tangible computer storage medium). As will be apparent from the foregoing examples, a computer-readable storage medium may retain information for a time sufficient to provide computer-executable instructions in a non-transitory form. Such computer-readable storage media or media may be transportable, so that the program or programs stored thereon may be loaded onto one or more different computers or other processors. And various aspects of the invention as discussed above can be implemented. As used herein, the term “computer-readable storage medium” encompasses only non-transitory computer-readable media that may be considered a product (ie, an article of manufacture) or a machine. Alternatively or additionally, the invention may be embodied as a computer readable medium other than a computer readable storage medium, such as a propagated signal.

  The term “program” or “software” refers to any type of computer code or program that can be employed to program a computing device or other processor and implement various aspects of the invention as discussed above. Used herein in a general sense to refer to a set of computer-executable instructions. In addition, according to one aspect of this embodiment, when executed, one or more computer programs that perform the disclosed methods need not reside on a single computer or processor, It should be understood that various aspects of the present disclosure may be implemented in a modular fashion distributed between different computers or processors.

  Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

  The vehicle control methods and structures described above may be implemented in a number of different applications and environmental situations. For example, although the embodiments described below were performed in idealized conditions and / or still water, the methods and vehicles described herein may be stationary or turbulent as can be expected in the ocean. Any of the conditions can be implemented through the use of appropriate control and / or feedback loops.

Example: Simulation of ground effect induced by lateral movement In order to explore how fluid flow affects the vehicles described herein, the flow around the vehicle is a standard from ANSYS. Simulated using standard CFX, static CFD software. For a simulated vehicle moving at 0.5 m / sec, the Reynolds number is about 40,000, based on which the κε turbulence model was selected. A fine (high density) mesh was used in the gap area between the vehicle and the corresponding surface. The remaining volume was meshed using standard default settings. Mesh quality was tested by increasing the mesh density until the density (number of nodes) was doubled, resulting in lift and drag changes of less than 10%. Buoyancy was not included.

  A simulation was performed at 5 mm to confirm the expected flow and pressure patterns associated with the vehicle traversing laterally across the surface. Specifically, the high speed under the vehicle caused a pressure drop. However, the leakage of flow in the y direction rapidly decreased the magnitude of the flow velocity before reaching the outlet. This non-uniform flow and pressure distribution caused higher pressure at the rear than at the front, resulting in a nose-down pitching moment. However, zero pitch can be achieved through underbody design as well as active control through pressure jets.

In addition to confirming the flow pattern and kinetics, the expected lift and suction forces were calculated. Referring to FIGS. 20 and 21, the simulation results identified 3 flow forms using ε = h / c.
1) ε ≦ 0.01 in region (a) with positive lift
2) 0.01 ≦ ε ≦ 0.3 in region (b) with negative lift

  3) ε ≧ 0.3 in the region (c) where the ground effect force is no longer significant

  20 and 21 show simulation results for a vehicle moving at a speed of 0.5 m / sec over various gap lengths. When very close to the surface and below 2 mm (region a), lift acts on the vehicle. The vehicle is stable at 2 mm and all forces are balanced. Above 2 mm (region b), the Venturi force pulls the vehicle toward the ground, but there is a second equilibrium point around 50 mm. However, this is an unstable point of equilibrium (ie a positive slope). Thus, if the vehicle is displaced away from the equilibrium point, this will continue to leave the equilibrium point due to ground effect forces that do not bias it back. Above 50 mm, there is again a net lift, which spans large distances as the body smoothly transitions to free flow behavior.

The transition from region (a) F _z > 0 (lift) to region (b) Fz <0 (suction force) occurs around 2 mm where Fz = 0. A negative slope at this point makes it a stable equilibrium position. Specifically, positive z displacement results in Fz <0, while negative displacement results in Fz> 0. Therefore, the vehicle is returned to Fz = 0 point. In contrast, at a Fz = 0 point around 50 mm, a positive z displacement results in a positive Fz and pushes the vehicle further away, correspondingly a negative z displacement causes the negative Fz to This will suck the vehicle further down. The disappearance of the force at 2 mm combined with a large negative slope (ie a large restoring force) is particularly useful as this may allow the vehicle to stabilize in a small gap using only hydrodynamics. .

FIG. 22 shows CFD simulations for operation at 1 mm, 1.5 mm, 2 mm, 2.5 mm, 5 mm, and 6.5 mm at speeds ranging from 0.4 m / sec to 1 m / sec. It is observed that the lift follows v ² as expected for turbulence. Drag (not shown) also varies as ^{v 2.} Speed independent drag and lift coefficients were therefore used instead of force versus speed for modeling purposes.
Example: Stability analysis

Although the vehicle is stable at its equilibrium point, in some cases it is desirable to know the maximum perturbation in z that the vehicle can withstand while correcting itself. FIG. 24 presents a graph of velocity and displacement calculated for a vehicle with a mass m of 2.2 kg moving laterally with respect to the surface at 0.5 m / sec. The resilience used in the model was:

The system was modeled as a spring mass system with a spring constant k equal to the restoring force. Therefore, the resonance frequency was calculated as follows.

  The vehicle was then subjected to a displacement of 1 mm from equilibrium. The figure shows that the displacement and speed are slowly attenuated and oscillates near zero when the vehicle is automatically returned to the equilibrium position.

If the vehicle is perturbed to have a velocity v _z , the applied kinetic energy ½ mv _z ² moves the vehicle by a distance h ′ and the kinetic energy is stored in the stored potential energy ½ kh ′ ² . equal. If the applied kinetic energy exceeds the potential energy, it can be stored without exceeding the gap distance, and so on.

This can result in the vehicle touching the surface unless an active thrust is applied to the vehicle. This may be a concept that can be used to determine when the vehicle is actively controlled when it is perturbed from a stable equilibrium position. For example, the above relationship can be rearranged to provide:

Therefore, if the natural frequency of the vehicle at a particular location relative to the surface, multiplied by the gap distance, is less than the magnitude of the vehicle's speed relative to the surface, active thrust is applied to the vehicle toward the desired location. Can force the vehicle back and slow down, avoiding grounding. Alternatively, instead of height, this relationship may be used to determine when to apply active thrust to the vehicle and to keep the vehicle within a desired location threshold distance.
Example: Size effect analysis

Next, the effect of size on the dynamics of vehicles subject to ground effects was investigated. For this simulation, all dimensions were scaled by a constant of 1/2 and 2 compared to a normal 1x size vehicle. FIGS. 25 and 26 present the dimensionless lift coefficient C _L calculated for different sized vehicles at 0.5 m / sec and 1.0 m / sec. From this figure, C _L is considered to be a function of epsilon, it is substantially independent of the size and speed. Deviations observed in C _L at higher speeds and sizes may correspond from laminar flow through the gap transition to turbulence. Using an appropriate scale factor, this means that as the size increases, the force-to-mass ratio of the vehicle decreases. However, the maximum speed perturbation a vehicle can experience is independent of size if the gap is scaled as well. In addition, the resonant frequency decreases for larger sizes, allowing more time for the control system to respond. In addition, ground effect forces and associated slopes are also considered to increase with size, suggesting that it may be desirable to increase the corresponding balance gap of the vehicle as well.
Example: Test of ground effect induced by lateral movement

FIG. 23 presents experimental lift data for a vehicle suspended using a hollow steel rod connected to an ATI force and torque sensor in a water filled tow tank. Various tests were performed in 1 mm, 1.5 mm, 2 mm, 5 mm, and 6.5 mm gaps from the platform and in free flow. The test speed was varied from 0.1 m / sec to 1 m / sec and in addition steady. Both drag and lift were measured and compared to the CFD results shown in FIG. FIG. 23 presents the measured lift minus the free flow force to facilitate comparison with the corresponding CFD data. Experimental data points measured from variable speed and gap were overlaid with a quadratic fit for force versus speed. The most prominent feature shown in FIG. 23 is lift in a 1 mm gap, especially at a speed of 1 m / sec. However, the force is very small for all speeds at 1.5 mm. Above 1.5 mm, negative lift (venturi effect) occurs. Beyond 6 mm, this negative force begins to disappear. FIG. 27 presents corresponding experimental data for drag F _{x at} different gaps and velocities overlaid with second order fits.

Figures 28 and 29 present a comparison of drag and lift coefficients calculated from CFD and the experimental data noted above, in good agreement.
Example: Vehicle for testing of jet-induced ground effect forces

The vehicle had an elliptical body with a single 5 mm diameter cylindrical nozzle located at the center bottom of the vehicle. A simple centrifugal pump powered by 0-12V was mounted inside and the flow passed through a short tube (15 mm long) to the nozzle. The voltage versus flow characteristics for the pump are shown in FIG. The effective working area of the pump was 3-12V, with a maximum head pressure of 30 kPa at 12V. For these experiments, the vehicle had a net underwater weight of 3 gf (grams per gram) or 0.03 N in water. In free flow, the jet produced forces from 0.0007 N (at 3V) to 0.036 N (at 12V). Thus, there is one setting, and only one, where the jet thrust alone counters the downward force from the weight. This is an equilibrium condition for any depth away from the surface. This behavior is here similar to that of a neutral suspension. Thus, a slight increase in thrust will raise the vehicle and a slight decrease will cause it to sink. This is therefore in a neutral equilibrium state.
Example: Test of ground effect force induced by jet

FIG. 31 presents lift versus clearance distance from the surface for a pump functioning at 12V (ie, 0.036 N). As can be seen in this figure, the vehicle has a fluid film-based behavior in which pressure builds up in region 1 to a level above the free flow thrust under the vehicle, and the jet-induced lift loss reaches maximum suction. Transition to region 2 which starts to prevail so as to reduce the lift. The fountain effect then begins to dominate and increases the lift in region 3 until it exceeds the free flow thrust. The lift then decays to free flow thrust at longer distances in free flow conditions.
Example: Simulation of ground effect force induced by jet

  Since the theory of lubrication is relatively deeply understood, the simulation was limited to a turbulent model of a jet oriented downward toward the surface in an underwater environment, somewhat similar to vertical and takeoff and landing simulations. The model was set up using CFX, a standard static CFD software from ANSYS. Turbulence was handled by the κ-ε model. The mesh was generated using “Proximity and Curve” for advanced size functions, resulting in a dense mesh around the bottom of the vehicle, especially when close to the surface. The pump is represented by an inlet at the top of the pipe and the inlet flow rate is set to match the measured characteristics of the pump noted above. The simulation confirmed the suction phenomenon for the flow rate corresponding to the total power (12V) at a gap size of 100 mm and 20 mm, respectively. Specifically, both the expected downward flow of the body and, for small gaps, both a low pressure region just below the body that forms a ground vortex is observed. The simulation also confirmed that the blow-up from the jet impinging on the surface changes direction and escapes from the lower edge of the vehicle, resulting in additional lift observed from the fountain effect.

  FIG. 32 presents lift versus clearance distance from the surface, calculated for different voltages applied to the pump and correspondingly different jet velocities. As can be seen in this figure, the lift curve behaves similar to that shown in FIG. However, as the voltage decreases, i.e., as the jet velocity decreases, the peak fountain effect decreases steadily to a smaller gap size until the fountain effect is overwhelmed by suction at a sufficiently low voltage / velocity. Moving. FIG. 32 presents similar data on net lift from the surface versus gap distance measured for different voltages applied to the pump ranging from 5V to 10V in 1V increments.

Note that FIG. 32 includes a correction for variable cable length (for pump power) immersed in water. However, the stiffness of the cable is not included in the model. Thus, although there is a qualitative agreement with the measured value, as calculated by the model, a stable equilibrium in the distance that varies with the pump power is consistent with the measured stable distance and the corresponding Does not quantitatively match the voltage.
Example: Measuring the stability point of a vehicle

  A vehicle with a net weight of 3 gmf was placed on the aquarium floor in 2 feet of water. Because it is heavier than water, the body remained in contact with the bottom of the aquarium. Even though the bottom jet was powered at 3 volts, the vehicle remained in contact with the surface. As the voltage was increased, the vehicle tended to swing, which was interpreted as due to incomplete meshing of the two surfaces. The fluid leached out of the nozzle and formed a film below the vehicle. This was evident when the vehicle was tapped. When the jet is turned off, the vehicle will hardly move. In contrast, when the jet was powered, the vehicle moved smoothly and over a considerable distance, demonstrating a simple demonstration of lubrication theory where both the lubricating fluid and the propagation medium are water.

The vehicle was then attached to a force sensor and suspended above a 5 foot deep aquarium floor. An ultrasonic rangefinder was used to measure the distance between the vehicle and the floor. When the pump was powered at 10V, 4.5 feet above the floor, the jet thrust balanced the weight of the robot, ie the force sensor read zero. To check if the vehicle behavior was overwhelmed by ground effects, the vehicle was lowered to a depth of 4 feet, keeping the pump powered at 10V. The vehicle maintained a neutral equilibrium at that height as well, indicating that the ground was not the dominant factor. However, at 3.5 feet, the vehicle suffered an upward force that pushed it back to 4 feet. In addition, when the vehicle was again placed at 4.5 feet and the voltage was reduced to 8 volts, the vehicle began to sink as expected but continued to stabilize at 3.5 feet. As the voltage was further reduced, the vehicle sank correspondingly to a new stable equilibrium point with respect to the surface. This was observed up to 4V, in which the vehicle was stable at 2 feet from the surface. These measurements were repeated 5 times. The measured stable balance point versus pump voltage is shown in FIG. In addition, as shown in FIG. 35, the free flow thrust at each voltage is calculated using the pump characteristics, which are then used to calculate the corresponding blowing force at each stable point, Was then normalized to thrust.
Example: Control thruster design

  Figures 36 and 37 depict a thruster layout for an elliptical vehicle with dimensions 203mm x 152mm with a flat bottom. The resulting aspect ratio is about 4: 3, which can improve the controllability of the vehicle. Of course, the size can be adjusted either smaller or larger to accommodate various types of electronics and sensors. As shown in this figure, the vehicle has six thrusters or jets. Specifically, there are four “propulsion jets” (J1, J2, J5, J6) and two “pressure jets” (J3, J4). The propulsion jet is oriented at an inward angle of γ in the xy plane, which determines the yaw-way dynamics of the system. While non-zero γ can help improve the controllability of the system in the absence of friction, a zero angle can also be used. Regarding the stability on the horizontal plane, which was the first test case, the center of gravity (CG) of the vehicle was located below the buoyancy. This was done by placing the ballast at the bottom of the robot. For more complex cases (eg, inspecting a vertical wall or circling around a pipe), it may be desirable to adjust the CG location as described above. Note that the jets J1, J2, J5, and J6 can be oriented at an angle β such that they pass through the CG of the system. This can help reduce or eliminate thrust-induced vehicle pitching. However, friction or surface curvature may still require active pitch control of the vehicle. This pitch control can be provided using two pressure jets J3 and J4 oriented vertically upwards at an angle α, as shown in FIG.

  Two vehicles with different jet arrangements were tested in contact mode with a surface traversed across the surface while the vehicle was in contact with the surface.

  A first vehicle with two non-angled pressure jets and four non-angled propulsion jets was tested by placing it on a horizontal surface in water, making it slightly heavier than neutral buoyancy. 38 and 39 are photographs of the exterior and interior of the vehicle. In this photograph, the vehicle has an elliptical body with a flat bottom and the non-angled jet is distributed around its surface. The internal picture shows the arrangement of pumps, valves and hydraulic connections used to power the four propulsion jets. During the test, when jets J1 and J2 were turned on and the vehicle was propelled horizontally, the vehicle suffered a nose down pitch and proceeded in a circle instead of moving forward. In FIGS. 40 and 41, when the vehicle yaws, the vehicle can be seen in a nose-down pitched position at a small angle θ. While not being bound by theory, this first vehicle had a straight jet, so the length of the moment arm to the center of gravity resulted in a pitch-down moment. Frictional force from the ground contact also contributed to the pitch-down moment. Furthermore, drag could not compensate for this effect due to the low lateral speed of the vehicle relative to the surface. Thus, it was observed that the Munch moment combined with an accidental skid perturbation resulted in a constant yaw rate and the vehicle traveled in a circle.

The second vehicle tested also included propulsion and pressure jets as discussed above. In addition, in order to help counter the pitching induced by the thrust observed in the first vehicle, the jet was oriented at an angle β, reducing the moment arm of the propulsion jet relative to the CG. For simplicity, β is chosen so that the force vector passes through the estimated center of gravity of the vehicle, thereby reducing the pitch caused by placing the jet in the upper half of the vehicle otherwise. Minimized (see FIGS. 42 and 43). During the test, the vehicle did not pitch when jets 1 and 2 were turned on. However, the vehicle yawed due to the Munch moment. To help compensate for this effect, a simple PD controller and closed loop response check was implemented. FIG. 44 shows a comparison of the closed loop and open loop trajectories of a vehicle on a low friction glass surface (μ _k <0.3). As can be seen in this figure, for a given friction, a simple PD controller was able to control the yaw angle normally. Note that for very high friction, the Munch moment will face a braking torque that will substantially reduce the yaw rate.

Although the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art. Therefore, the foregoing description and drawings are merely examples.

Claims (25)

A method for controlling a vehicle immersed in a fluid, comprising:
Positioning the vehicle immersed in a fluid at a first preselected distance relative to a surface;
Applying a ground effect to the vehicle to maintain the vehicle at the first preselected distance;
Including a method.   The method of claim 1, wherein applying a ground effect force to the vehicle includes moving the vehicle laterally relative to the surface.   The method of claim 1, wherein applying a ground effect force to the vehicle includes applying a thrust directed toward the surface.   The step of applying ground effect force to the vehicle includes both moving the vehicle laterally with respect to the surface and applying a thrust directed toward the surface. The method described in 1.   The method of claim 1, wherein the ground effect force urges the vehicle toward a first preselected distance relative to the surface as the vehicle is displaced relative to the surface.   When the vehicle is at the first preselected distance, the net weight of the vehicle and the ground effect force are substantially zero applied to the vehicle in a direction oriented toward the surface. The method of claim 1, wherein the method provides force.   The method further comprises modifying the ground effect force to move the vehicle from a first preselected distance relative to the surface to a second preselected distance relative to the surface. Item 2. The method according to Item 1.   The method of claim 1, further comprising scanning the surface with a sensor as the vehicle is moved laterally relative to the surface.   9. The method of claim 8, wherein the first preselected distance is within a desired sensing range of the sensor.   Applying to the vehicle a thrust that urges the vehicle toward the surface, the net weight of the vehicle when the vehicle is at the first preselected distance, a thrust toward the surface And the ground effect force results in a substantially zero force applied to the vehicle in a direction oriented toward the surface. A method for controlling a vehicle immersed in a fluid, comprising:
Applying the ground effect force to the vehicle at a first stable equilibrium distance of the ground effect force relative to a surface, so that when the vehicle is displaced relative to the surface, the ground effect force is Urging the vehicle toward the first stable equilibrium distance.   The method of claim 11, wherein applying a ground effect force to the vehicle includes moving the vehicle laterally relative to the surface.   The method of claim 11, wherein applying a ground effect force to the vehicle includes applying a thrust directed toward the surface.   12. The step of applying a ground effect force to the vehicle includes both moving the vehicle laterally relative to the surface and applying a thrust directed toward the surface. The method described in 1.   The method of claim 11, further comprising scanning the surface with a sensor as the vehicle is moved laterally relative to the surface.   The method of claim 15, wherein the first stable equilibrium distance is within a desired sensing range of the sensor.   The method of claim 11, further comprising modifying the ground effect force to move the vehicle from a first stable equilibrium distance to the surface to a second stable equilibrium distance to the surface. . A method for controlling a vehicle immersed in a fluid, comprising:
Orienting a flat portion of the vehicle toward a surface;
Applying a thrust force to the vehicle to urge the vehicle toward the surface;
Applying a ground effect force to the vehicle against the surface, the net weight of the vehicle, a net thrust force urging the vehicle toward the surface, and a ground effect force associated with the surface, Providing a substantially net force applied to the vehicle in a direction oriented toward the surface;
Including a method.   When the vehicle is at a first preselected distance relative to the surface, the net weight of the vehicle, the thrust that biases the vehicle toward the surface, and the ground effect force associated with the surface are: The method of claim 18, wherein the method provides a substantially net force applied to the vehicle in a direction oriented toward a surface.   20. The method of claim 19, wherein the first preselected distance is a first stable equilibrium distance with respect to the surface.   The method of claim 18, wherein orienting the flat portion of the vehicle toward the surface further comprises adjusting a center of gravity of the vehicle to orient the flat portion of the vehicle toward the surface. .   The method of claim 18, wherein applying a ground effect force to the vehicle includes moving the vehicle laterally relative to the surface.   The method of claim 18, wherein applying a ground effect force to the vehicle includes applying a thrust directed toward the surface.   The step of applying ground effect force to the vehicle includes both moving the vehicle laterally with respect to the surface and applying a thrust directed toward the surface. The method described in 1.   The method of claim 18, further comprising scanning the surface with a sensor as the vehicle is moved laterally relative to the surface.